[C++-sig] create boost array from a Numpy PyArray without copying data? (original) (raw)
Sebastian Walter walter at mathematik.hu-berlin.de
Mon Jan 19 13:16:10 CET 2009
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Hello, On the C++ side I have a raw pointer: double *x; I'd like to change its values from within Python by using Numpy. Example code can be found below.
My approach is
- make PyArray from existing data *x with PyArray_SimpleNewFromData
- create a boost array from the PyArray.
My question is: How can I create a boost::python::numeric::array from a Numpy Pyarray without copying data?
Here my best shot... (compiles and runs but copies the data)
- ----------------- test.cpp ------------------
#define PY_ARRAY_UNIQUE_SYMBOL PyArrayHandle #include #include <boost/python.hpp> #include <numpy/noprefix.h>
using namespace std; using namespace boost; using namespace boost::python; using namespace boost::python::numeric;
array test_function(){ int N = 3; double x[] = {1.,2.,3.}; array numpy_x(static_cast(handle<>(PyArray_SimpleNewFromData(1, &N, PyArray_DOUBLE, x)))); double *y = static_cast<double*> PyArray_DATA(numpy_x.ptr()); y[0] = 37.;
for(int n = 0; n<N; ++n){
cout<<"numpy_x[n]="<<y[n]<<"\t\t"<<"x[n]="<<x[n]<<endl;
}
return numpy_x;}
BOOST_PYTHON_MODULE(_test) { import_array(); array::set_module_and_type("numpy", "ndarray"); def("test_function", test_function); }
- ----------- test.py ----------------- from _test import *
if name == "main": print test_function()
- --------------- shell output -------------------- $python test.py numpy_x[n]=37 x[n]=1 numpy_x[n]=2 x[n]=2 numpy_x[n]=3 x[n]=3 [ 37. 2. 3.]
It would be great if anyone knew the answer to my problem.
regards, Sebastian Walter -----BEGIN PGP SIGNATURE----- Version: GnuPG v2.0.4-svn0 (GNU/Linux) Comment: Using GnuPG with SUSE - http://enigmail.mozdev.org
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